Asphalt-based roofing systems and products are well known. They include, for example, asphalt shingles and asphalt roll roofing. Many conventional materials are utilized as raw materials in the manufacture of asphalt roofing systems and products.
Asphalt roofing systems and products generally comprise a substrate which is filled and coated with various asphalt materials. Generally, the substrate is filled with a "saturant" asphalt. A saturant asphalt is oil-rich and relatively non-viscous, to provide maximum waterproofing and saturation of the substrate. The saturant asphalt serves as a preservative, a waterproofing agent and an adhesive agent.
The saturated substrate is sealed by application of a harder, more viscous "coating" asphalt to both sides of the substrate. Coating asphalts generally contain finely divided minerals therein as stabilizers or fillers. Such compounds as silica, slate dust, talc, micaceous materials and dolomite have been utilized as fillers to render the coating asphalt more shatter-proof and shock-proof in cold weather.
The exterior, outer, or exposed surface of asphalt roofing systems and products is generally provided with a covering of granular material or roofing granules embedded within the coating asphalt. The granular material generally protects the underlying asphalt coating from damage due to exposure to light, in particular ultraviolet (UV) light. That is, the granules reflect light and protect the asphalt from deterioration by photodegradation. In addition, such granular material improves fire resistance and weathering characteristics. Further, colors or mixtures of colors of granular material may be selected for aesthetics.
In general, the mineral materials, particles or granules are embedded within the coating asphalt under pressure and are retained therein by adherence to the asphalt. With respect to each granule, the asphalt may be viewed as a "hot sticky mud" into which the granules are pressed. When the asphalt cools, pockets having the granules retained therein are formed.
Good adherence of the roofing granules to the roofing product is beneficial. Loss of granules reduces the life of the roof, since it is associated with acceleration of photodegradation of the asphalt. In addition, the aesthetics of the roofing system may be compromised if granules are lost. Further, reduction of granule loss during installation improves safety conditions on the roof.
Granule loss can also occur due to physical abrasion of the granular surface. This may occur any time a person walks on an installed roof for maintenance, during installation of the roofing surface or by such environmental conditions as tree branches rubbing on the granular surface and the physical contact of rain or hail with the roofing surface.
It has been found that adherence between the roofing granules and the coating asphalt is subject to deterioration by moisture. Granule-asphalt adhesion is not well understood. However, it is probable that secondary bonding interactions contribute to adhesive bond strength. Disruption of this secondary bonding by moisture may lead to decreased adhesion of granules to asphalt. Although water run-off from a slanted roof is generally sufficient to avoid prolonged exposure to moisture and thus to avoid substantial degradation by moisture to the granule/asphalt bond or interface, problems from moisture deterioration nevertheless pose substantial risk. For example, deterioration may be substantial in humid environments or in relatively flat portions of roofs where water can collect. Further, in many instances bundles of shingles (or similar roofing material) are stored in plastic wraps or containers prior to installation. Moisture trapped within such wraps or containers may cause substantial deterioration of the granule/asphalt bond, with resultant reduction in the integrity of the later installed roofing surface.
Prior to applicants' improvements to the adhesion of roofing granules to the roofing product, it was generally felt that granule asphalt adhesion was satisfactory. It is, however, clear from the above discussion that beneficial results may be achieved by improving the granule asphalt adhesion in roofing products. What has been needed has been a method of improving asphalt-based roofing systems having granular material embedded therein with respect to granule loss due to moisture attack compromising the granule/asphalt bond or interface. In addition, improved roofing materials with respect to photodegradation of the asphalt layer by preventing granule loss by physical abrasion have been desired.